ActiveRecord inconsistency on changes method

test.rb

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  gem "rails", github: "rails/rails"
  gem "arel", github: "rails/arel"
  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.string :title
  end
end

class Post < ActiveRecord::Base
  def title
    super.upcase
  end
end

class BugTest < Minitest::Test
  def test_changes
    post = Post.create!(title: 'hey')
    post.title = 'ho'

    assert_equal(['hey', 'ho'], post.changes["title"])
  end
end